This invention relates to a fret-saw machine provided with a blade holder unit of an improved structure for holding a fret-saw blade and with a blade cover and other associated members capable of carrying out effective cutting work and performing an improved operation.
Generally, a fret-saw machine is provided with an elongated fret-saw blade which is set substantially perpendicularly with respect to a flat surface of a work table on which a workpiece is placed and the workpiece is cut by reciprocally driving the fret-saw blade.
The fret-saw machine generally comprises a base table, a driving unit suspended from the rear surface side of the base table to be swingable, an arm member generally having a U shape and having one end secured to a frame member disposed in the base table, an upper holder unit secured to the other end of the U-shaped arm member above the base table, a lower holder unit operatively connected to a motor accommodated in the driving unit at a portion below the base table, and a fret-saw blade having longitudinal ends held by the upper and lower holder units. In such arrangement, the fret-saw blade is adjusted in its position so that the fret-saw blade can be moved in a direction perpendicular to the plane of the base table surface when a workpiece is cut by the fret-saw blade.
Furthermore, in such arrangement, the fret-saw blade is fastened to the machine body by fastening means such as a bolt and nut assembly or the like, inconveniently requiring a loosening or clamping the bolt and nut assembly when removing or attaching the fret-saw blade to the holder units.
In such prior art, there is provided a fret-saw machine in which the fret-saw blade can be adjusted in its positioning angle, for example, as disclosed in the Japanese Utility Model Publication No. 57-13202, which, however, discloses a structure capable of adjusting the blade attaching angle only to a predetermined angle. Therefore, it is desired to provide a fret-saw machine having an improved structure capable of adjusting the blade attaching angle to a desired optional angle.
In the foregoing, there is described a fret-saw machine in which the fret-saw blade is held substantially perpendicularly with respect to the table surface on which the workpiece to be cut is placed, and the blade supported at its both ends by the upper and lower holder units to be vertically movable. However, in such arrangement, there is a case where cut chips are not easily removed, and in some cases, vertical cut lines may be formed on the cut surface of the workpiece, thus providing bad finishing, and in the worst case, the blade operation may be stopped while the blade is in engagement with the workpiece being cut.
In order to obviate such defect, there is also provided a structure for driving the blade. Namely, a pair of parallel upper and lower arm members are swingably attached to both the end portions of the blade. According to such arrangement of the parallel swingable arms, the reciprocal motion of the blade has a component perpendicular to the table surface and a component parallel thereto during the cutting operation of the blade.
However, the structure of a fret-saw machine having such a fret-saw swinging mechanism makes the precise angular positioning of the fret-saw blade complicated, and the manufacturing thereof is also made complicated, requiring much time and labor.
Furthermore, in the fret-saw machine, it is necessary to stretch the fret-saw blade between the upper and lower blade holders with a predetermined tension for cutting work. In a prior art, one end, i.e. the following blade holder side opposing the blade drive side, of the blade is pulled to apply tension to the blade and is secured while the blade is under tension. However, in the prior art technique, it is difficult or troublesome to adjust the fastening of the screw bolt to obtain a desired tension, resulting in complicated work for an operator, thus requiring an improved blade tensioning device or assembly.
Still furthermore, in the fret-saw machine of the prior art, when it is required to change the lateral inclination of the blade with respect to the base table on which the workpiece to be cut is placed, the fastening screw is first loosened and the screw shaft is shifted along the arcuate shape of the hole into which the screw shaft is fitted thereby to move the U-shaped arm around the shaft, thus changing the lateral inclination of the blade holder unit together with the blade. However, in such arrangement, the U-shaped arm is generally secured to the frame member at its lower end portion and to the holder unit at its upper end portion, so that the positioning of the blade between the upper and lower holder units by adjusting the position of the arm is made difficult.
Still furthermore, the fret-saw blade is generally covered by a blade cover which is capable of being rotated for attaching or removing the blade, and a workpiece is supported by a pressing member for preventing the workpiece from being shifted during the cutting working, this pressing member being disposed as a separate member from the blade cover. In the conventional blade cover, there is a fear of accidental rotation of the blade cover during the cutting working, and a blade fastening structure for reliably fastening the blade cover to its holder member is also required.